1. Field of the Invention
The present invention relates to a light shutter device and a driving method thereof, and more particularly to a light shutter device which has light shutter elements made of a material with an electro-optical effect such as PLZT to write an image on a photosensitive recording medium and a method of driving such a device.
2. Description of Related Art
As means of writing an image (latent image) on a silver salt photographic paper or film or on a photosensitive member for electrophotography, there have been suggested various kinds of light shutter devices which employ light shutter elements made of a material with an electro-optical effect such as PLZT and which turn on and off the light shutter elements individually.
In such a light shutter device, when a voltage is applied to a PLZT light shutter element, the PLZT causes birefringence, and light which is incident to the element via a polarizer located before the element is emergent from an analyzer located after the element. The polarizer and the analyzer are arranged to cross Nicol (are arranged in such a way that the direction of polarization of the polarizer and the direction of polarization of the analyzer will cross at 90 degrees to each other). The plane of polarization of the polarizer and the plane of polarization of the analyzer are at 45 degrees to the direction of electric field acting on the light shutter element.
In order to write a full-color image, color filters of R, G and B, which are the three primary colors, are switched in order during irradiation of the light shutter elements, so that a silver salt film is exposed to light of R, light of G and light of B separately line by line.
Incidentally, as FIG. 11 shows, with respect to a light shutter element made of PLZT, the relationship between light transmittance and voltage applied thereto changes according to whether the light is of red, green or blue. The voltage to achieve the maximum light transmittance is referred to as a half-wave voltage. Supposing that the half-wave voltages for red light, for green light and for blue light are Vr, Vg and Vb respectively, Vr>Vg>Vb. In order to obtain a full-color image of high quality, the driving voltage of the light shutter elements shall be switched to Vr, Vg and Vb for red, green and blue, respectively.
In Japanese Patent Laid Open Publication No. 10-333107, the Japanese applicants suggested a device which switches the voltage applied to the driver IC for the light shutter elements in synchronization with the light incidence of the three primary colors. However, the switching of a high voltage to be applied to the driver IC is influenced by the capacity of a bypass capacitor or the like, it is difficult to switch the voltage at a high speed.